1. Field of the Invention
This invention generally relates to spas and hot tubs and more specifically to control systems and circuits for the heaters utilized in such spas and hot tubs.
2. Description of the Related Art
Whirlpool spas and hot tubs typically include a tub for holding water, a pump for circulating the water and a heater. Usually the pump draws in water from the tub, forces it through the heater and out through jets in the tub, thereby circulating the water and causing it to be heated by passing it through the heater. For safety purposes, the heater is typically provided with some type of flow sensor control device that allows the heater to only operate when water is flowing through the system. In addition, the heater also typically includes a thermostat control device and a high limit temperature control device which turns the heater off if the temperature of the water exceeds a safe limit, such as 119.degree. F.
Safety regulations often require that the high limit temperature control operate such that when it is tripped, it must be re-set, much like a circuit breaker. That is unlike, for example, the flow sensor control which can cycle on and off repeatedly in response to water flowing and not flowing through the system. In most current heaters, there are simple electromechanical controls which are responsive to the lack of water flow, excessive temperature and act as a thermostat. These are typically configured as a circuit including the heater element, a bimetallic thermostat, a bimetallic high limit thermostat and a pressure or flow switch, all connected in series with a source of line voltage, typically 115 volts AC. The bimetallic thermostat is configured to turn on and off in response to the temperature of the water. The bimetallic high limit thermostat is configured to trip when the high limit temperature is exceeded. The bimetallic high limit thermostat must be manually re-set after it has been tripped. When the pump is activated by an air switch or an electronic switch, water flows through the heater and activates the flow switch. This allows power to flow through the thermostat switches and the heater.
A shortcoming of such a system is that when an over temperature condition occurs, which can be due to the filling of the bathtub with hot water over the maximum temperature of the high limit thermostat, the high limit thermostat will "trip" and disconnect the heater. The heater will not operate until the high limit thermostat is reset. Frequently, the heater is located underneath the tub without easy user access. Also, typically there is no visible indication that the high limit thermostat has been tripped. Often the user does not realize that the high limit thermostat has been tripped and instead believes the system is broken.